The importance of annealing in tuning the morphology and thus the properties of organic-inorganic hybrid membranes becomes more and more realized. In this study, novel organic-inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and gamma-(glycidyloxypropyl) trimethoxysilane (GPTMS) were prepared through in situ sol-gel approach. To elucidate the effect of annealing temperature and annealing time on swelling and sorption properties as well as pervaporation properties of PVA-GPTMS hybrid membranes, the free volume characteristics of the membranes were systematically analyzed by positron annihilation lifetime spectroscopy (PALS). Furthermore, the effects of feed composition and operating temperature on pervaporation proper-ties of annealed membranes were also investigated. (c) 2006 Elsevier B.V. All rights reserved.